Horatio Chapple, 17, was sleeping on a glacier near the Arctic Circle when the starving 39st beast dragged him from his tent and caused “mortal wounds” to his head.

The roaming bear injured four others before a member of the expedition group finally shot it dead.

Failures, including the faulty tripwire system with missing parts replaced by paperclips, were highlighted in a report released yesterday to coincide with an inquest.

The inquiry by Sir David Steel for the British Schools Exploring Society, which organised the expedition, said a “bear watch” guard was most likely to have prevented the rare attack at Svalbard, Norway, in 2011.

A tripwire system that was in place should have set off a blast as the bear approached to warn the camp but was wrongly positioned and missing crucial parts.

Horatio’s group also had three mines instead of four around their site.

In addition, the rifle used to shoot the bear failed to fire initially.

Sir David said: “This tragedy was caused by the rare occurrence of an intrusion of a starving polar bear into a camp situated well inland in Svalbard. It was remote possibility.”

Horatio’s mum, Dr Olivia Chapple, a GP from Bishopstone, Wilts, told the inquest she thought all the group would be armed with pen flares to scare away bears, yet only leaders had them.

She said of organisers: “I trusted all the things they had listed were going to happen – otherwise I would never have let Horatio go.”

Expedition leader Richard Payne said he was “ultimately responsible” for the safety of the 73 children on the expedition.

He said he had never encountered a polar bear before, adding: “To have one in that area at that time of year and behave as it did was totally out of character.”